Permanent magnet electrical machines are advantageous for use in applications where high torque (when used as a motor) or high power (when used as a generator) are required, but the machine is also required to be small, light and to have high efficiency. Applications for such machines include land vehicles, aircraft, water-borne vessels and fixed industrial applications.
Permanent magnet electrical machines have a ring of permanent magnets and a ring of magnetic coils (often called windings), usually disposed within slots in an armature of low permeability material, such as laminated iron. The magnetic coils commonly form a ring on a stator around a rotor which carries the permanent magnets, but other arrangements are possible. Turning the rotor relative to the stator creates currents in the coils, allowing the electrical machine to be used as a generator. Conversely, alternating current can be applied to the coils to cause the rotor to turn, allowing the electrical machine to be used as a motor.
Electrical machines of this type commonly have a large number of permanent magnets and coils and this leads to high frequency losses connected with the coils, particularly relating to eddy currents within the coils.